The present invention relates generally to carburetors for internal combustion engines, and more specifically to internally vented float bowl carburetors.
In a typical float bowl type carburetor, fuel flows from the reservoir in the float bowl through a fuel metering orifice into a fuel well from which the fuel is drawn up and mixed with air due to the pressure differential caused by the venturi region in the carburetor bore or throat. Since a continuous flow of fuel from the float bowl to the venturi must be provided in order to assure smooth engine operation, it is necessary to maintain a consistent fuel level in the float bowl. In order to maintain a consistent fuel level, a float control valve arrangement is provided such that as the fuel level in the float bowl is depleted through normal operation, the float control valve opens a conduit connected to a larger fuel storage tank. As fuel is replaced in the float bowl, an excess pressure is created above the fuel level. A proper fuel flow rate is facilitated by venting the excess pressure from the top of the float bowl to a constant pressure region. This venting may be to the atmosphere external of the carburetor (external venting) or to a region of relatively constant pressure within the carburetor bore (internal venting). Both types of venting arrangements are well known in the art.
Internally vented float bowl arrangements are advantageous to externally vented bowls in that air that is supplied to the vent has already passed through the carburetor air filter so that the likelihood of introducing additional contaminants into the carburetor is greatly reduced. In addition, in internally vented arrangements, as the air cleaner element becomes clogged and the pressure within the carburetor throat decreases, the pressure in the fuel bowl also decreases due to the passageway connecting the carburetor throat and the bowl, thereby leaning out the fuel-air mixture to a level proportional to the level that existed when the air cleaner element was unobstructed.
As government regulations require small internal combustion engines to limit exhaust gas emissions to a prescribed level, engines will be required to operate on a leaner fuel/air mixture than previously. Such leaner calibration requirements create difficulties in starting the engine. In engines operating on such leaner fuel/air mixtures, it may be necessary to prime and restart the engine several times before the engine temperature increases to the point where fuel is vaporized at a sufficient rate to permit sustained engine operation.
It is desired to provide an engine which operates on a leaner fuel/air mixture yet which can be started without excessive priming and/or startup attempts.